Read Callister, Chapters 15 and 16. Solve and hand in Problems 15.16, 15.22, 15.35, 15.44, 16.11, 16.18, 16.20, 16.22, due date Wednesday March 3.

Question 15.16

The tensile strength and number-average molecular weight for two polyethylene materials are as follows:

Tensile Strength MPa Num. Av. Mol. Wt.(gm/mol)
85 12,700
150 28,500

Estimate the number-average molecular weight that is required to give a tensile strength of 195 MPa.

Question 15.22

Which of the following would you expect to be elastomers and which thermosetting polymers at room temperature? Justify each choice.

  1. Linear and crystalline polyethylene
  2. Phenol-formaldehyde
  3. Heavily cross-linked polyisoprene having a glass-transition temperature of 50 C.
  4. Lightly crosslinked poly isoprens having a glass-transition temperature of - 60 C.
  5. Linear and partially amorphous polyvinyl chloride.

Question 15.35

During the winter months, the temperature in some parts of the Yukon may go as low as - 55 C. Of the elastomers natural polyisoprene, styrene-butadiene, acrylonitrile-butadiene, chloroprene and polysiloxane, which would be suitable for automobile tyres under these conditions? Why?

Question 15.44

If you want to produce nylon 6, 6 by condensation polymerisation using hexamethylene diamine and adipic acid, what masses of these two components will be needed to yield 20 kg of completely linear nylon 6, 6?

Question 16.11

A continuous and aligned fiber-reinforced composite is to be produced consisting of 30 vol% aramid fibres and 70vol% of a polycarbonate matrix. Mechanical characteristics of these two materials are as follows:

Modulus of Elasticity (GPa) Tensile Strength (MPa)
Aramid Fibre 131 3,600
Polycarbonate 2.4 65

Also, the stress on the polycarbonate matrix when the aramid fibres fail is 45 MPa. For this composite, compute (a) the longitudinal tensile strength and (b) the longitudinal modulus of elasticity.

Question 16.18

A continuous and aligned fibrous reinforced composite having a cross-sectional area of 970 mm2 is subjected to an external tensile load. If the stresses sustained by the fibre and matrix phases are 215 MPa and 5.38 MPa respectively, the force sustained by the fibre phase is 76,800 N and the total longitudinal composite strain is 1.56 * 10-3, then determine:

  1. the force sustained by the matrix phase
  2. the modulus of elasticity of the composite material in the longitudinal direction
  3. the moduli of elasticity for fibre and matrix phases

Question 16.20

Suppose you want to produce an aligned carbon fibre-epoxy matrix composite having a longitudinal tensile strength of 500 MPa. Calculate the volume fraction of fibres necessary if

  1. the average fibre diameter and length are 0.015 mm and 2.0 mm respectively; and
  2. the fibre fracture strength is 4.0 GPa and
  3. the fibre-matrix bond strength is 25 MPa and
  4. the matrix stress at composite failure is 7.0 MPa.

Question 16.22

  1. From the moduli of elasticity data in Table 16.2 for glass fibre-reinforced polycarbonate composites, determine the value of the fibre efficiency parameters for each of 20, 30 and 40 vol% fibres
  2. Estimate the modulus of elasticity for 50 vol% glass fibres.